This invention relates, in general, to heat transfer systems and, in particular, to a heat transfer system for transferring heat between a refrigerant and a heat storage medium to minimize operating costs of the system.
More specifically, but without restriction to the particular use which is shown and described, this invention relates to a heat transfer system wherein the indoor coil of a heat pump is in thermal contact with a heat storage medium forming a common heat exchanger to effect heat transfer between the components of the system.
As is well known to those skilled in the art of heat transfer, heat pumps function to move heat from one location to another. During cold weather, heat, which has already been produced outdoors by the sun and stored in the earth and air, is transferred to a heat-exchange fluid by an outdoor coil and carried indoors. In warm weather, the cycle is reversed. Warm air indoors is circulated about an indoor coil so that the heat from the indoor air is absorbed to the heat-exchange fluid, generally referred to as a refrigerant, which is then carried outdoors to the outdoor coil releasing the heat to the surrounding air.
Since a heat pump moves heat between the indoors and the outdoors, the system does not consume as much energy as a heating system that heats the indoors by heat generation. To further increase system efficiency, heat pumps are sometimes combined with other types of heat transfer systems such as solar collectors. The solar collectors transfer radiant heat from the sun to a heat storage medium, such as water, which is circulated through a finned coil in heat exchange contact with air passing over the fin surfaces. In such systems, if the heat transferred to the heat storage medium through the solar collectors is insufficient for heating purposes, the heat pump is energized to supplement the heat supplied from the storage medium. During cooling, the heat pump performs in a conventional manner by circulating refrigerant through a finned indoor coil in heat exchange contact with air being circulated over the fin surfaces of the coil.
Such combined heat transfer systems serve to reduce the overall cost of heating by utilizing the heat transferred through the solar collectors to the storage medium for heating purposes. However, due to variation in the amount of heat transferred to the storage medium through the solar collectors, such systems have not been entirely satisfactory. For example, if the amount of heat transferred to the storage medium through the solar collectors is frequently less than that required for heating purposes, the heat pump must be continuously operated to obtain the desired heating. In addition, such combined systems do not improve the efficiency of the heat transfer systems during cooling operation and do not provide for heat transfer between the heat pump coil and the heat storage medium.